Salmonellosis

Salmonellosis

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ICD-9	003.0
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Salmonellosis is the name name of a group of infectious diseases caused by bacteria of the genus Salmonella, including typhoid fever, paratyphoid fever, and food poisoning.

Salmonella

Salmonella are rod-shaped, gram-negative bacteria, whose main habitat is the intestinal tract of animals. As of December 7, 2005, there are two species within the genus Salmonella: Salmonella bongori (previously subspecies V) and Salmonella enterica (formerly called Salmonella choleraesuis), which is divided into six subspecies, such as Salmonella enterica subspecies enterica.

While only two species are recognized, there are numerous serotypes (or serovars). A serovar or serotype is a grouping of microorganisms (or viruses) based on their cell surface antigens, allowing differentiation below the level of species. Serovars may be established based on virulence factors, lipopolysaccharides in gram-negative bacteria, presence of an exotoxin, plasmids, or other characteristics that differentiate members of the same species (Barron 1996). Various accounts place the number of known serotypes as "over 2,200" (Breslow 2002) and around 4,400 (Ryan and Ray 2004).

However, only a few of these serotypes cause infections in humans, with the majority of cases traced to only five to ten common forms (Breslow 2002). The vast majority of human isolates (>99.5%) are subspecies S. enterica. For the sake of simplicity, the Center for Disease Control and Prevention (CDC) recommends that Salmonella species be referred to only by their genus and serovar, for instance, Salmonella typhi, instead of the more technically correct designation, Salmonella enterica subspecies enterica serovar Typhi.

Overview of salmonellosis

The type of salmonella usually associated with infections in humans is called Non-Typhoidal Salmonella. Food poisioning is the most common type of salmonella. It is caused by S. typhimurium or other serotypes. It is usually contracted by ingesting raw or undercooked eggs, or from improper handling of meat products. Common sources are:

• Poultry and cattle, if the meat is prepared incorrectly or becomes infected with the bacteria somehow.
• Infected eggs and milk, as well as egg products, when not prepared, handled, or refrigerated correctly.
• Reptiles such as turtles, lizards, and snakes, as they can carry the bacteria on their skin.

Non-typhoidal bacteremia (bacteræmia in British English, also known as blood poisoning or toxemia) is caused by S. enterica, S. typhimurium, or S. heidelberg in the blood.

A second, rarer general category of salmonella is called Typhoidal Salmonella. It is only carried by humans and is usually contracted through contamination with the fecal matter of an infected person. It therefore mainly occurs in countries that do not have proper systems for handling human waste. This kind of salmonella infection can lead to typhoid fever.

Typhoid fever (or enteric fever) is an illness caused by the bacterium Salmonella typhi (Salmonella enterica Serovar Typhi). Common worldwide, typhoid fever is transmitted by the feco-oral route, which incorporates ingestion of food or water contaminated with feces from an infected person. Transmission involving infected urine is possible, but much less common (Giannella 1996). According to the CDC, typhoid fever is common in most areas of the world except in industrialized regions such as the western Europe, United States, Canada, Japan, and Australia.

Paratyphoid fever is caused by infection of Salmonella paratyphi, and is also spread the feco-oral route.

Etymology

Both Salmonellosis and the Salmonella type of microorganisms derive their names from a modern Latin coining after Daniel E. Salmon 1850–1914, an American Veterinary surgeon. He had help from Theobald Smith, and they found the bacterium in pigs in 1885.

Symptoms

In food poisioning, the bacterium induces responses in the animal that it is infecting and this is probably what causes the symptoms rather than any direct toxin. Most persons infected with Salmonella develop diarrhea, fever, vomiting, and abdominal cramps 6 to 72 hours after infection. Headache, fatigue, and rose spots are also possible. In most cases, the illness usually lasts 3 to 7 days.

Most affected persons recover without treatment. However, in some persons the diarrhea may be so severe that the patient becomes dangerously dehydrated and must be taken to a hospital. At the hospital, the patients will receive intravenous fluids to treat their dehydration and medications may be given to provide symptomatic relief, like fever reduction. In severe cases, the Salmonella infection may spread from the intestines to the blood stream, and then to other body sites and can cause death unless the person is treated promptly with antibiotics. The elderly, infants, and those with impaired immune systems are more likely to have a severe illness.

Some people afflicted with salmonellosis later experience reactive arthritis (Reiters Syndrome), which can have long-lasting, disabling effects (Dworkin et al. 2001). In sickle-cell anemia, osteomyelitis due to Salmonella infection is much more common than in the general population.

See typhoid fever for a detailed discussion of the symptoms and treatment of that disease.

Incidents of salmonellosis

See typhoid fever for discussion of that disease.

The CDC (2006) notes that about 40,000 cases of food poisoning are reported every year in the United States alone, but that mild cases are not usually reported or diagnosed and that actually cases of salmonellosis may be 30 times that number or more. Breslow (2002) notes that only an estimated one percent of cases in the United States are even reported.

One of the largest outbreaks of food poisioning occurred in the United States in 1985, when an estimated 185,000 people were infected from drinking improperly pasteurized milk (Breslow 2002). In 1998, there were over 800 cases of S. enteritidis in Canada traced to a pre-packed lunch product (Breslow 2002).

In June 2006, the British Broadcasting Company (BBC) reported that the Cadbury chocolate manufacturer withdrew a number of products because of possible contamination with salmonella (BBC 2006). The problem had been traced to a leaking pipe at a Cadbury plant in Herefordshire in January 2006, though the announcement was not made until June.

In March 2006, The New York Times reported that the U.S. government said that 16.3% of all chickens were contaminated with salmonella. In the mid to late twentieth century, Salmonella enterica serovar Enteritidis was a common contaminant of eggs. This is much less common now with the advent of hygiene measures in egg production and the vaccination of laying hens to prevent salmonella colonization. Many different salmonella serovars also cause severe diseases in animals other than human beings.

Breslow (2002) reports that current concern regarding salmonellosis is centered on the emergence of multiple antibiotic resistent salmonella, which will make serious illness difficult to treat.

References

ISBN links support NWE through referral fees

• Baron, E. J. 1996. Classification. In S. Baron et al., eds., Baron's Medical Microbiology, 4th edition. University of Texas Medical Branch. ISBN 0963117211.
• Breslow, L. 2002. Encyclopedia of Public Health. New York: Macmillan Reference USA/Gale Group Thomson Learning. ISBN 0028658884.
• British Broadcasting Company (BBC). 2006. Cadbury recall after health fears. BBC News, June 23, 2006. Retrieved April 10, 2007.
• Centers for Disease Control and Prevention. 2005. Outbreak of multidrug-resistant Salmonella Typhimurium associated with rodents purchased at retail pet stores: United States, December 2003-October 2004. Morbidity and Mortality Weekly Report. Retrieved April 9, 2007.
• Centers for Disease Control and Prevention. 2006. Salmonellosis. CDC Division of Bacterial and Mycotic Diseases. Retrieved April 10, 2007.
• Dworkin, M. S., P. C. Shoemaker, M J. Goldoft, and J. M. Kobayashi. 2001. Reactive arthritis and Reiter's syndrome following an outbreak of gastroenteritis caused by Salmonella enteritidis. Clin Infect Dis 33(7): 1010-14. PMID 11528573.
• Giannella, R. A. 1996. Salmonella. In S. Baron et al., eds., Baron's Medical Microbiology, 4th edition. University of Texas Medical Branch. ISBN 0963117211.
• Ryan, K. J., and C. G. Ray (editors). 2004. Sherris Medical Microbiology, 4th ed. McGraw Hill. ISBN 0838585299.

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